<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <div class="somecontent"></div>
    <div class="leftnav">
        <ul>
            <li></li>
            <li></li>
            <li></li>
            <li></li>
            <li></li>
            <li></li>
            <li></li>
        </ul>
    </div>

    <div class="floor f1"></div>
    <div class="floor f2"></div>
    <div class="floor f3"></div>
    <div class="floor f4"></div>
    <div class="floor f5"></div>
    <div class="floor f6"></div>
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    <div class="somecontent"></div>
</body>
</html>